I am currently running a 2014 13'' rMBP. I recently tried to delete a Bootcamp partition in Disk Utility. When I tried to reboot my system, it did not boot OS X (Mojave) and instead could only boot to the (empty) Bootcamp partition. I followed klanomath's advice in this article, and articles like it. I found out using dd if=/dev/disk0s2 count=3 | vis -c that my original partition with the bootable OS X was an APFS partition.

A suppose you should post the output from the command sudo dd if=/dev/disk0 count=1 skip=409640 | hexdump -Cv. You will need to disable System Integrity Protection (SIP) before executing the command.
– David AndersonMar 24 at 18:30

Note: The sudo may not be required. You may need to disable System Integrity Protection (SIP) before executing the commands. Older versions of gpt will require substituting 7C3457EF-0000-11AA-AA11-00306543ECAC for apfs.